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Friday, March 09, 2007

Navy gun talk. 57mm to 155mm and all the fun non-metric Medium Caliber Guns (MCG) out there. Nice summary from a Brit site here. Worth a full read - but you can see the reasons behind the 57mm for LCS and the 155 for DDG-1000.

The MCG also has the advantage of providing a more measured response than missiles, which is likely to prove increasingly important in the kind of United Nations or NATO "police actions '' in which the Western navies are frequently engaged today. An anti-ship missile is an all-or-nothing weapon. A gun can fire warning shots or inflict limited damage in order to persuade a recalcitrant ship's captain of the error of his ways without going so far as to sink his ship. The same measured response can also be used in shore bombardment as was done in South Georgia, at the start of the Falklands conflict, when Argentine positions were bracketed in a display of force but deliberately not hit (the conflict had yet to become "hot").

For such limited "demonstration" actions it doesn't really matter what sort of gun is fitted, as long as there is one. At present, the 76mm OTO Melara continues to dominate in international sales but the 57mm Bofors is beginning to catch up, particularly in the USA (a previous 76mm user) where the Bofors has been selected for all three of the Coast Guard Cutter, DD(X) and Littoral Combat Ship programmes. In Russia, the St Petersburg "Arsenal" plant is expected to finish, by the end of 2005, trials of a new 57mm gun (designated A-220) with a rate of fire 300 rpm, intended for patrol boats. However, there is still strong interest in larger-calibre weapons for NGS, in the immediate future focused on 127mm guns but with the prospect of even larger calibres later on. The problem is that when it comes to serious naval action, the best type of MCG to have depends entirely on the circumstances and these cannot be predicted in advance. This suggests that a general-purpose weapon, with some capability in all possible roles, would be the best choice.

The most impressive Western MCG is probably still the 120mm Bofors - one wonders what it would be capable of today if its development had been continued. Of the current weapons, the French Creusot-Loire 100mm Compact has a lot to offer. The 13.5 kg shell is significantly lighter than the 21 kg of the British 4.5" or the 31.7 kg of the American 5", but the 90 rpm rate of fire is four times as fast as the British weapon and the gun system is claimed to have anti-missile capability. Rather surprisingly, it seems to have been almost ignored in terms of international sales.

The best contender for current warships is probably the 127mm OTO Melara, as it combines the most powerful ammunition (the American 5") with a reasonably high rate of fire. It is the closest Western weapon to the formidable Russian 130mm twin mounting. It is therefore the best choice for the anti-ship and shore bombardment roles, particularly as shore bombardment missiles, other than the extremely expensive Tomahawk, are a long way from service. Italy has selected a new lightweight version of this mounting for its next generation of warships, featuring a 64-calibre barrel but with the rate of fire reduced to 35 rpm (clearly, the requirements of land attack are now dominating). For now, the Royal Navy has adopted a modified (all-electric mounting) version of the 4.5" Mk 8 and developed an extended-range (27 km) base-bleed shell, although a 155mm gun is (or at least was) pencilled in for later batches of the new Type 45 destroyer.

Also of interest are the need to make sure your gun is multi-purpose.

So which philosophy is correct; small calibre and high rate of fire or larger, slower-firing guns? The Falklands conflict provided evidence to support both viewpoints. The shore bombardment role (NGS = Naval Gunfire Support) was clearly important, with the 4.5" guns firing some 8,000 rounds. On the other hand, there was a desperate need for more close-range AA fire in the confined arena of San Carlos Water, where the 76mm OTO Melara or particularly the 57mm Bofors would have been in their element. Curiously, the 4.5" Mk.8 fire control system was reportedly optimised for AA fire and was not well designed for NGS, with four crewmen needed in the command centre to operate the weapon.

Also, some very interesting European concepts.

In Europe, the Italians and the Dutch are combining to develop the Vulcano, a fin-stabilised dart-shaped sub-calibre (HEFSDS) GPS/INS guided 127mm round with a range of 120 km, also for the NGS role. This is a one-piece round which can be fired at 35 rpm - the new OTO-Melara lightweight gun (in either 54 or 64 cal versions) can also fire ERGM at 17 rpm. There is also a project for a simpler unguided 127mm 13 kg fin-stabilised round which has a muzzle velocity of 1,200 m/s to give it a range of 70 km.

The Italians are also developing a subcalibre DART ammunition for the 76mm gun (rather similar in appearance to APFSDS tank gun rounds), to be launched at 1,200 m/s and intended to be effective against anti-ship missiles. There must be some concern, however, about the effectiveness of what must be a small (proximity-fuzed) warhead given the very high closing speeds. A 'hit-to-kill' mode would seem preferable, but as the chosen guidance method is an RF beam-rider, it is probably not accurate enough for that at longer ranges.